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rav65819_ch08_143-164 - *142 Chapter 8 Photosynthesis...

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***142 Chapter 8 Photosynthesis introduction THE RICH DIVERSITY OF LIFE that covers our Earth would be impossible without photosynthesis. Almost every oxygen atom in the air we breathe was once part of a water molecule, liberated by photosynthesis. All the energy released by the burning of coal, firewood, gasoline, and natural gas, and by our bodies’ burning of all the food we eat—directly or indirectly—has been captured from sunlight by photosynthesis. It is vitally important, then, that we understand photosynthesis. Research may enable us to improve crop yields and land use, important goals in an increasingly crowded world. In chapter 7, we described how cells extract chemical energy from food molecules and use that energy to power their activities. In this chapter, we examine photosynthesis, the process by which organisms such as the aptly named sunflowers in the picture capture energy from sunlight and use it to build food molecules that are rich in chemical energy. concept outline 8.1 Overview of Photosynthesis Photosynthesis combines CO 2 and H 2 O, producing glucose and O 2 In plants, photosynthesis takes place in chloroplasts 8.2 The Discovery of Photosynthetic Processes Plants do not increase mass from soil and water alone Photosynthesis includes both light-dependent and light-independent reactions O 2 comes from water, not from CO 2 ATP and NADPH from light-dependent reactions reduce CO 2 to make glucose 8.3 Pigments Light is a form of energy Each pigment has a characteristic absorption spectrum 8.4 Photosystem Organization Production of one O 2 molecule requires many chlorophyll molecules A generalized photosystem contains an antenna complex and a reaction center 8.5 The Light-Dependent Reactions Some bacteria use a single photosystem Chloroplasts have two connected photosystems The two photosystems work together in noncyclic photophosphorylation ATP is generated by chemiosmosis Thylakoid structure reveals components’ locations 8.6 Carbon Fixation: The Calvin Cycle
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Calvin cycle reactions convert inorganic carbon into organic molecules Carbon is transferred through cycle intermediates, eventually producing glucose 8.7 Photorespiration Photorespiration reduces the yield of photosynthesis C 4 plants have evolved to minimize photorespiration The crassulacean acid pathway splits photosynthesis into night and day ***143 8.1 Overview of Photosynthesis Life is powered by sunshine. The energy used by most living cells comes ultimately from the Sun, captured by plants, algae, and bacteria through the process of photosynthesis. The diversity of life is only possible because our planet is awash in energy streaming Earthward from the Sun. Each day, the radiant energy that reaches Earth equals about 1 million Hiroshima-sized atomic bombs. Photosynthesis captures about 1% of this huge supply of energy (an amount equal
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rav65819_ch08_143-164 - *142 Chapter 8 Photosynthesis...

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